bottom-dwellers in shallow coastal waters (usually less than 300
feet or 100 metres); exclusively marine, inhabiting warm temperate and
tropical parts of the western and eastern Pacific and western Indian
oceans

a single genus (Heterodontus) in the family Heterodontidae

A
representative heterodontoid, the Port Jackson Shark (Heterodontus
portusjacksoni), showing the characteristic deep nasoral
grooves, small mouth with thick labial (lip) cartilages, pronounced
brow ridges, stout spine in front of each dorsal fin, and the
presence of an anal fin. Like all bullhead sharks, adults of the
Port Jackson have teeth that are strongly differentiated in both
jaws: peg-like grasping teeth in the front, molar-like crushing
teeth in the rear. The body markings shown here are unique to the
Port Jackson Shark, consisting of a saddle-like pattern mid-flank
and a dark stripe under each eye. These eye stripes (called 'Malor
stripes') are believed to reduce glare as the shark swims over
highly reflective bottoms, in much the same way that footballers and
soldiers reduce glare by applying grease paint under their eyes.

The heterodontoids just don't get the respect they deserve as card-carrying,
union-member sharks. It's not their fault — they are victims of their own
appearance. Bullhead sharks have a pig-like snout and a small puckered mouth, a
surprised expression punctuated by bovine brow-ridges, and a chubby little body
sparkling with over-sized scales. Bullheads move with an endearing clumsiness —
either clambering over the bottom on large, paddle-like pectoral fins or
swimming with an exaggerated wriggle, resembling fat-bellied pollywogs. An
embodiment of piscine cuteness, bullheads seem an ideal antidote to the
pernicious image with which all sharks have been saddled since JAWS.

Dorsal
fin skeleton of a Horn Shark (Heterodontus francisci) showing the
stout fin spine and reduced fin skeleton — compare this illustration with
that of the Spiny Dogfish fin
skeleton). Fin spines were common in many ancient sharks, and have
independantly evolved in two lineages of modern sharks, the bullheads
(order Heterodontiformes) and the dogfishes (order Squaliformes).

Heterodontoids are nocturnally active predators;
juveniles feed on buried
worms, adults on small fishes, crustaceans, and molluscs. Bullhead shark table
manners range from unrefined to downright comical. When consuming hard-shelled
invertebrate prey, bullheads typically grind up the food and swallow it — shell
and all — regurgitating the hard parts later. Off California, the Horn Shark (Heterodontus
francisci) has a definite predilection for red sea urchins, which often results
in its teeth being stained reddish-brown - like the tongue of a child that has
just finished a grape popsicle. Horn sharks apparently also appreciate
interactive novelty snacks, as some have been observed to 'pounce' on sea
anemones, nipping off a mouthful of tentacles before the hapless invertebrate
could retract them.

Horn Shark (Heterodontus francisci)

As its name suggests, the Galapagos Horn Shark
(Heterodontus quoyi) is endemic to the Galapagos Islands and other
islands off Peru. Growing to a length of 22 inches (57 centimetres), it is
most active at night and feeds heavily on crabs. This species is often
observed resting on ledges of vertical rock faces at depths of 50 to 100
feet (15 to 30 metres). Despite its defensive dorsal spines, one small
specimen was found in the stomach of a Tiger Shark (Galeocerdo cuvier).

Bullheads are smallish sharks, the various species growing to lengths of 4 to
5.6 feet (1.2 to 1.7 metres). Their modest size renders bullheads vulnerable to
predation. The characteristic fin spines of bullheads are an effective
anti-predator device, discouraging larger fishes from eating these snack-sized
sharks. On several occasions, Pacific Angel Sharks (Squatina
californica) off
California have been filmed swallowing juvenile Horn Sharks, only to disgorge
them with much haste and what looks for all the world like abject disgust. There
is even a report from Australia of a Port Jackson Shark (Heterodontus
portusjacksoni) stuck in the mouth of a dead wobbegong, which was apparently
asphyxiated by its prickly last meal.

Auger-shaped eggcase of a Horn Shark (Heterodontus francisci)

The egg cases of bullhead sharks are among the most
wonderfully bizarre in all of Nature. They are auger-shaped: more-or-less
conical and surrounded by two broad spiral flanges. This shape enables a
mother bullhead to wedge her eggs (usually laid two at a time) into
crevices, preventing removal by most would-be predators without benefit of
opposable thumbs. The Crested Bullhead, (Heterodontus galeatus) has egg
cases with a pair of tendrils, which readily tangle around kelp
structures, anchoring them. The Japanese Bullhead (Heterodontus
japonicus)
apparently uses communal nesting sites — with as many as 15 eggs deposited
in the same patch — using them as a kind of heterodontoid day care. Due to
their awkward shape, each bullhead egg case requires several hours to
rotate out of the mother shark's cloaca. Even in the very serious matter
of perpetuating their lineage, heterodontoids are less-than-dignified.

Bullhead eggs hatch after a gestation period of 5 to 12 months, depending
upon species and water temperature. Size at birth varies with species, ranging
from 5.5 to 9.5 inches (14 to 24 centimetres) in length. Recent studies by
Wesley Strong off California indicate that adult horn sharks utilize a home
range of up to 10,760 square feet (1,000 square metres); tagging studies in
eastern Australia have revealed that the Port Jackson Shark makes annual
migrations of up to 525 miles (850 kilometres) along the coast. Bullheads do
well in private and public aquaria, the Horn Shark both breeding and holding the
record for longevity in captivity at 25 years.

Like the rest of their bodies, the
pronounced brow-ridges that give the bullhead sharks their vernacular name
are covered with large dermal denticles. Those individuals that
habitually rest with their heads under rock or coral ledges often have
their brow-ridge denticles polished smooth. Others — like this Horn
Shark (Heterodonts francisci) — that rest with their heads al
fresco, have rough, unabraded denticles atop their brow-ridges.